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400-007 · Question #164

Which design benefit of bridge assurance is true?

The correct answer is D. It prevents switch loops caused by unidirectional point-to-point link condition on Rapid PVST +. Bridge Assurance prevents switching loops caused by unidirectional link failures on point-to-point links by requiring continuous bidirectional BPDU exchange on all designated and root ports in Rapid PVST+.

Designing Network Infrastructure

Question

Which design benefit of bridge assurance is true?

Options

  • AIt supposes a spanning-tee topology change upon connecting and disconnecting a station on a
  • BIt prevents switched traffic from traversing suboptimal paths on the network.
  • CIt allows small, unmanaged switches to be plugged into ports of access switches without the risk
  • DIt prevents switch loops caused by unidirectional point-to-point link condition on Rapid PVST +

How the community answered

(43 responses)
  • A
    2% (1)
  • B
    5% (2)
  • C
    2% (1)
  • D
    91% (39)

Why each option

Bridge Assurance prevents switching loops caused by unidirectional link failures on point-to-point links by requiring continuous bidirectional BPDU exchange on all designated and root ports in Rapid PVST+.

AIt supposes a spanning-tee topology change upon connecting and disconnecting a station on a

Suppressing topology change notifications when a station connects or disconnects is the function of PortFast, not Bridge Assurance.

BIt prevents switched traffic from traversing suboptimal paths on the network.

Preventing traffic on suboptimal paths describes the effect of STP root bridge placement and path cost tuning, which are separate spanning tree design concerns.

CIt allows small, unmanaged switches to be plugged into ports of access switches without the risk

Preventing risk from unmanaged switches plugged into access ports is the function of BPDU Guard, which disables a port upon receiving any BPDU.

DIt prevents switch loops caused by unidirectional point-to-point link condition on Rapid PVST +Correct

Bridge Assurance continuously sends BPDUs on every active spanning tree port, and if a port stops receiving BPDUs - as occurs during a unidirectional link failure - it transitions to a bridge assurance inconsistent blocking state, preventing a loop from forming. This specifically targets the failure scenario where a link physically forwards in one direction only, which traditional STP mechanisms cannot reliably detect before a loop forms on Rapid PVST+ point-to-point links.

Concept tested: Bridge Assurance preventing unidirectional link loops in Rapid PVST+

Source: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/CLIConfigurationGuide/SpanningTreeBridgeAssurance.html

Topics

#bridge assurance#STP#Rapid PVST+#unidirectional link

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